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Microlenses and infrared optical components: from fabrication towards novel interferometric characterization

Friday, 12 December, 2008 - 15:30
Campus: Brussels Humanities, Sciences & Engineering campus
Virginia Gomez Onate
phd defence

The general trend in optics and micro-optics in particular is to miniaturize and to fabricate small, efficient and reliable photonic systems without overlooking the manufacturing cost. In recent years, due to their small size and coste effectiveness, micro-optical components can be found in CD readers, medical applications, scanning labels and mobile phones.

This PhD work is about microlens fabrication technologies and characterization techniques. In interferometry, light is used because of the achievable accuracy related to its wavelength. Moreover, the specimen is not damaged during the measurement process. In this PhD dissertation we focus on the Micro-Optic Reflection and Transmission Interferometer (MORTI) developed as a combination of a Mach-Zehnder and a Twyman-Green interferometer. Therefore, it enjoys the advantages of both interferometers in one instrument. Only one lens positioning is needed to measure all its characteristics. Besides, as the measurements can be done within minutes, the same environmental conditions are held.

In industrial fabrication processes, to control the quality and specifications of the microlens arrays, an off-line characterization is performed. Commonly, one microlens is then measured at random places in a large array or an inspection measurement over the complete wafer is done with low accuracy. As a consequence, the fabrication processes should be standardized and controlled to be able to fabricate the required microlenses without calibration iterations. In order to improve the reproducibility of the fabrication technologies, we developed an interferometric technique for the real time in situ monitoring of microlenses, that can be applied at fabrication level. The set-up and a case study on Deep Proton Writing technology are explained.

Due to the increasing interest in automotive, dark vision and space applications, semiconductor materials such as germanium, silicon and fused silica are becoming more and more important. These materials are transparent at infrared wavelengths. This wavelength region still lacks characterization and measurement tools. We present a Mach-Zehnder interferometer designed to work in transmission in the near infrared wavelength range. This interferometer solves the instrumentation gap that exists to characterize infrared components in transmission.

In collaboration with Umicore, the world leader company in the supply of materials for long wave infrared, we performed a study on the improvement of germanium as an optical infrared material. We explain all the technologies used for the characterization of germanium crystals, and the methods applied for improving its optical quality and macrolenses performance.

With this PhD dissertation we have opened the field of semiconductor microlenses characterization. We believe that the above mentioned research results will contribute to solving fabrication and characterization issues of refractive microlenses, and hence will support low-cost enhanced photonic-based products for the benefit of our society in general, and of our scientific and economic community in particular.